Installing engine space ventilation in a 1985 31 O'day

Nov 6, 2019
4
O'Day 31 Solomons, MD
Hi -- I have a 1985 O'day 31. Read on practical sailor a review of the O'day 30 - 31 class, and they suggested adding sound installation to the engine compartment to cut down on the noise and vibration. Has anyone installed ventilation for the engine space as well? As has been noted on other sailboats of the era, it gets hot in there and both the heat and fumes drift into the cabin.

If you have undertaken this project, how and where did you install your ventilation? Did you add an inline blower fan to exhaust it outside? Any help or helpful guidance is appreciated.
 
Nov 6, 2019
4
O'Day 31 Solomons, MD
I get the royalties if you use this.

A little bit overboard but a good winter project when I did it.
Wow @Ralph Johnstone, simply brilliant and perfectly detailed. You are indeed owed royalties!

It's thanks to good folks like you that I figured out and replaced the original engine issues stemming to terrible trailer lighting package used by the factory that melted down (and left you stranded unable to crank the engine over...let alone the fire hazard)
 
Jan 22, 2008
50
Oday 30 Stamford CT
Deja Vu II....I have a 1983 30' O'Day which is very similar to your boat. I installed sound proofing on the inside surface of the port and starboard wood panels, the forward removable engine access panel as well as the engine access panel in the quarter berth. The material I used is a thick foam rubber covered with a shiny aluminum protective cover. It reduced the sound coming into the boat but it is still louder than what I was expecting. I installed a Nico clamshell vent on the port and starboard side of the boat right behind the turning blocks and installed an inline blower that is connected to one of the clamshell vents. The inline blower is very load and I only run the blower if I'm doing a long run and the temperatures are high and I want to cool down the engine compartment.
 
Nov 6, 2019
4
O'Day 31 Solomons, MD
@GeorgeC you are exactly correct and have described the 31's engine space to a tee! I appreciate the response, especially sharing your experience on soundproofing, as well as venting the engine space. It sounds like I should have realistic expectations on reducing the sound in the cabin, but even modest improvements may please the +1/the admiral. I'm hopeful venting with the blower assist helps with the temperature on those hot days with long runs (for me, getting to the Chesapeake Bay). Did you find venting the heat and introducing more air helps with engine performance any?

I grew up as a navy brat going up and down the east coast on a 1983 30', it's a great boat, though the stern felt like climbing the side of a mountain as a kid getting out of the water after dad tossed us in on swim calls.

Deja Vu II....I have a 1983 30' O'Day which is very similar to your boat. I installed sound proofing on the inside surface of the port and starboard wood panels, the forward removable engine access panel as well as the engine access panel in the quarter berth. The material I used is a thick foam rubber covered with a shiny aluminum protective cover. It reduced the sound coming into the boat but it is still louder than what I was expecting. I installed a Nico clamshell vent on the port and starboard side of the boat right behind the turning blocks and installed an inline blower that is connected to one of the clamshell vents. The inline blower is very load and I only run the blower if I'm doing a long run and the temperatures are high and I want to cool down the engine compartment.
 
Jan 22, 2008
50
Oday 30 Stamford CT
Deja Vu II....I have not seen any difference in engine performance from installing the vents. It did reduce the temperature in the engine compartment and relieved my concerns about the heat impacting the fire extinguisher and the cleaning materials stored in that space. For years my engine was running hot (190F) on any long runs when cruising along running at 2,000-2,200 RPM. I thought the vents would help drop that temperature but it didn't. I spoke to someone at one of the engine parts suppliers and was told that the heat exchanger installed on my Universal 16 hp #5416 was technically adequate, but it was right at the border of being the undersized for my engine. I purchased a 3" diameter heat exchanger, which was the next size up from the one that came with my engine, and have never had a problem of the engine going above 160F.
 
Sep 11, 2015
147
Hunter 31 Marina del Rey
It is very difficult to starve an engine of oxygen, even if you have a relatively air tight enclosure. Best approach is to have a small opening between the engine compartment and the lazarette or if not practical, just install a vent at the stern. You do not need to force air through it. The logic is that when gaseous concentrations change, the gas molecules travel super fast to equalize the concentrations (feet per second). A better way to explain it is that when you fart, the smell quickly fills the room, through the clothes and without any blowers. Exactly the same happens if the oxygen concentration in the engine compartment drops... oxygen molecules from any adjacent spaces quickly find their way through the openings. A few square inches is enough, typically towards the lazarette. You do not need to exchange all the nitrogen, etc.

Ventilation makes more sense if you want to evacuate gaseous vapors quickly before they spread as is necessary with gas engines. It is also very hard and inefficient to use ventilation to lower the temperature (water based heat exchangers are much more efficient in heat transfer). Consider a car on the highway, where the engine makes probably 30-40 hp to drive at highway speeds, then the volume of air and the speed at which it hits the radiator and then compare that mass transfer to the tiny 3" fan. It is basically of no use.

Another factor is if you just want to cool the alternator (a much easier task) but again, if you think about the mass volume/temperature difference vs. the heat generated by the alternator... it is hard to believe significant heat exchange occurs. A better way would be to blow cold air towards the alternator or consider liquid cooling but that is complicated.

In summary, unless you plan to make your compartment air-tight, I would not worry about it and spare the effort. If for some reason your engine dies out of oxygen starvation then you can reconsider but I think it is highly unlikely.